<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .box{
            /* normal是400 bold大概是700 值范围是1到1000 */
            font-weight: 800;
        }
    </style>
</head>
<body>
    <div class="box">我是div元素</div>
</body>
</html>